Re: [dpdk-dev] Big spike in DPDK VSZ

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 11-Feb-20 8:11 AM, David Marchand wrote:
> Hello Anatoly,
> 
> On Tue, Feb 4, 2020 at 11:23 AM Burakov, Anatoly
> <anatoly.burakov@intel.com> wrote:
>>
>> On 30-Jan-20 8:51 AM, David Marchand wrote:
>>> On Thu, Jan 30, 2020 at 8:48 AM siddarth rai <siddsr@gmail.com> wrote:
>>>> I have been using DPDK 19.08 and I notice the process VSZ is huge.
>>>>
>>>> I tried running the test PMD. It takes 64G VSZ and if I use the
>>>> '--in-memory' option it takes up to 188G.
>>>>
>>>> Is there anyway to disable allocation of such huge VSZ in DPDK ?
>>>
>>> *Disclaimer* I don't know the arcanes of the mem subsystem.
>>>
>>> I suppose this is due to the memory allocator in dpdk that reserves
>>> unused virtual space (for memory hotplug + multiprocess).
>>
>> Yes, that's correct. In order to guarantee memory reservation succeeding
>> at all times, we need to reserve all possible memory in advance.
>> Otherwise we may end up in a situation where primary process has
>> allocated a page, but the secondary can't map it because the address
>> space is already occupied by something else.
>>
>>>
>>> If this is the case, maybe we could do something to enhance the
>>> situation for applications that won't care about multiprocess.
>>> Like inform dpdk that the application won't use multiprocess and skip
>>> those reservations.
>>
>> You're welcome to try this, but i assure you, avoiding these
>> reservations is a lot of work, because you'd be adding a yet another
>> path to an already overly complex allocator :)
> 
> Went and looked at the EAL options we have.
> I understand that the --in-memory (essentially the --no-shconf
> functionality) option should be enough.
> I can see that Siddarth uses it.
> 
> But the problem is that the memory allocator still reserves big va
> areas for memory hotplug.

Yes, because even though we don't *share* this memory, we still grow it 
dynamically. We could have *not* done it, but that would be adding 
another code path - currently, we're piggybacking off existing 
infrastructure.

> 
> 
>>
>>>
>>> Or another idea would be to limit those reservations to what is passed
>>> via --socket-limit.
>>>
>>> Anatoly?
>>
>> I have a patchset in the works that does this and was planning to submit
>> it to 19.08, but things got in the way and it's still sitting there
>> collecting bit rot. This may be reason enough to resurrect it and finish
>> it up :)
> 
> Does this patchset contain more than just taking --socket-limit into account?

No, it actually doesn't rely on any of the existing options. It has to 
do with tweaking the config options related to memseg list sizings 
(essentially like adjusting config options at compile time, only without 
hardcoding them).

> 
> 
> --
> David Marchand
> 


-- 
Thanks,
Anatoly